Embryo development and survival

ABSTRACT

An embryo that is transferred into the uterus of a recipient female is protected from embryotoxic effects of prostaglandin F 2α  by exposing the embryo to a prostaglandin antagonist.

It is hereby acknowledged that the U.S. Government has certain rights in the invention described herein, which was supported in part by grants 94-37203-0722 and 99-35208-8402 from USDA-NRICGP.

FIELD OF THE INVENTION

The invention pertains to the field of in vitro fertilization and embryo transfer. In particular, the invention pertains to the field of transferring an in vivo-produced or an in vitro-produced embryo into the uterus of a female human or other mammal.

BACKGROUND OF THE INVENTION

Embryonic loss is a serious problem in the dairy and beef cattle industries, with the majority of these losses occurring during the first week of pregnancy, the period when the non-compacted morula is developing into the hatched blastocyst. Such embryonic losses are typically associated with factors in the oviduct or uterine environment that alter or inhibit embryonic development and/or function of the corpus luteum.

In cattle, these early embryonic losses occur in pregnancies that result from artificial insemination or from natural service. These losses also occur in pregnancies that result from embryo transfer. It is believed that embryonic losses following embryo transfer may be related, at least in part, to manipulation of the reproductive tract with resultant release of an embryotoxin during placement of the embryo in the uterus.

During the embryo transfer procedure in cattle, an embryo is placed in the uterine horn ipsilateral to the corpus luteum. This process requires manipulation of the reproductive tract, including handling of the cervix. It has been reported that such manipulation results in release of prostaglandin F_(2α). (PGF_(2α)) into the lumen of the uterus. Wann and Randel, J. Anim. Sci. 68:1389-1394 (1990); Odensvik et al, Acta. Vet. Scand. 34:219-221 (1993). PGF_(2α) is a natural luteolytic substance which is secreted by a female and which, in the absence of pregnancy, ends one estrous cycle in the female animal by destroying the corpus luteum and allows the next cycle to begin. Work in our laboratory has demonstrated that even minimal manipulation of the reproductive tract during embryo transfer results in release of PGF_(2α). Schrick, FN, et al, “Prostaglandin F_(2α) Appears to Directly Influence Early Embryonic Survival in Cattle: Would Administration of Flunixin Meglumine be Beneficial During Embryo Transfer?”, in Proceedings of the American Embryo Transfer Association, pp 9-16, Sacramento Calif. (2000).

Several studies have implicated PGF_(2α) as an embryotoxin during the very early time period of pregnancy. Schrick et al, Biol. Reprod., 49:617-621 (1993) reported elevated concentrations of PGF_(2α) in the uterine lumen of postpartum cows compared to normally cycling cows. The increase in uterine PGF_(2α) in these cows was related to the recovery of lower quality embryos compared with cows producing lower levels of PGF_(2α). Seals et al, Prostaglandins 56:377-389 (1998) reported that administration of PGF_(2α) to progestin-supplemented cows between days 5 and 8 of pregnancy caused decreased pregnancy rates compared to saline controls. However, the administration of PGF_(2α) on days 10 to 13 or days 15 to 18 had no effect on pregnancy rates. Further studies by Fazio and Schrick, Biol. Reprod. 56 (Suppl. 1): 187 (1997); Hernandez-Fonseca et al, J. Anim. Sci. 75 (Suppl. 1):221 (1997); and Donaldson, Vet. Rec. 118:661-663 (1986) indicate that PGF_(2α) has a detrimental effect on embryonic survival by decreasing the quality of embryos and reducing the developmental rate or ability of an embryo to develop beyond the morula stage.

The deleterious effect of PGF_(2α) on embryonic survival was further established by Schrick et al, Theriogenology 55(1):370 (2001) who reported a study that showed that the administration of a PGF inhibitor to recipient cattle at the time of embryo transfer results in an improvement of pregnancy rates. In this study, the prostaglandin inhibitor flunixin meglamine (BANAMINE, Schering Corp., Kenilworth, N.J., USA) was injected intramuscularly into recipient cattle immediately prior to or after non-surgical transfer of an embryo into the uterine horn ipsilateral to the corpus luteum. Pregnancy rates were significantly higher in cows receiving the prostaglandin inhibitor than in controls.

Thus, the prior art discloses that PGF_(2α) has a deleterious effect on embryonic survival in cattle by reducing the quality of embryos and the developmental rate or ability of an embryo to develop beyond the morula stage. The prior art further discloses that this deleterious effect of PGF_(2α) may be reduced by treatment of a recipient cow with a prostaglandin inhibitor at about the time of embryo transfer, thus effectively reducing the level of PGF_(2α) to which the embryo is exposed.

Similar deleterious effects of PGF_(2α) on embryonic survival and the reduction of this deleterious effect by treatment of the recipient female have been established for mammalian species other than cattle, including humans. See for example, Wollenhaupt, K., and Steger, H, Arch Exp. Veterinarined., 35(3):471-480 (1981); Waldenstrom, U, et al., Fertility and Sterility, 81(6):1560-1564 (2004); and Rubinstein, M., et al., Fertility and Sterility, 71(5):825-829 (1999).

A significant need exists for ways of reducing embryonic loss following embryo transfer in animals and humans, and especially for ways of reducing such loss without necessitating additional treatment of the recipient (surrogate) female.

DESCRIPTION OF THE INVENTION

It has been unexpectedly discovered that pre-treating an embryo with a prostaglandin antagonist prior to transfer of the embryo to the uterus of a recipient female animal provides a protective benefit to the embryo against the embryotoxic effects due to exposure of the embryo to PGF_(2α) in the uterus of the recipient animal. The invention is useful in embryo transfer in humans and other mammals to provide an increase in percentage of transferable embryos, pregnancies, and live offspring.

In one embodiment, the invention is a method for protecting an embryo to be transferred to the uterus of a recipient female animal. According to this embodiment of the invention, the embryo is exposed to a prostaglandin antagonist before transfer of the embryo to the uterus.

In another embodiment, the invention is a medium for holding, collecting, freezing, culturing, or transferring an embryo, or for maturation of an oocyte that is to be fertilized to produce an embryo, which embryo is to be transferred into the uterus of a recipient female animal. According to this embodiment, the medium contains a prostaglandin antagonist in addition to components necessary for the holding, collecting, culturing, freezing, or transferring or embryos or for maturation of oocytes that are to be fertilized and transferred.

In another embodiment, the invention is a method for performing embryo transfer. According to this embodiment, an embryo is transferred into the uterus of a female animal wherein, prior to the transfer, the embryo has been exposed to a prostaglandin antagonist.

In another embodiment, the invention is a non-human embryo that is protected against the embryotoxic effects due to exposure to PGF_(2α). According to this embodiment, the embryo was exposed to a prostaglandin antagonist during the time that the embryo was situated outside of the uterus of a recipient female animal.

As used herein, the term “exposure” as it pertains to a prostaglandin antagonist and an embryo or an oocyst refers to the exposure of an embryo or oocyst to the prostaglandin antagonist by other than by administering the prostaglandin antagonist to a recipient female with concomitant exposure of an embryo to the prostaglandin antagonist due to circulation of the administered prostaglandin antagonist to the uterus of the female. Such “exposure” by administration to the recipient female animal is not included within the present invention or within the meaning or the term “exposure” as used herein. Exposure of an embryo to a prostaglandin antagonist by infusion of the prostaglandin antagonist into the uterus of a recipient female is included within the present invention and within the meaning of the term “exposure”.

As used herein, the term “protect” means to defend an embryo against the direct and/or indirect embryotoxic effects of PGF_(2α) and thus inhibit the death, retardation, or reduction in development of embryos exposed to PGF_(2α). The use of the term “protect” does not mean or imply a guarantee that embryos will not be killed or otherwise harmed when exposed to PGF₂, or other factors. Rather, as used herein, this term means that the death rate of embryos due to exposure to PGF_(2α) is reduced or development of embryos is normal in the face of exposure to PGF_(2α) when the embryos are exposed to a prostaglandin receptor antagonist in accordance with the invention as compared with the death rate or abnormal development of embryos exposed to PGF_(2α) but not exposed to the prostaglandin receptor antagonist. Because it is impractical to test any particular embryo to determine if the embryo is “protected”, it is conceived that such protection may be determined by historical or statistical means.

As used herein, “placement or transfer of an embryo into the uterus” of a recipient female animal includes such placement or transfer into other portions of the female reproductive system that are utilized in embryo transfer, such as into the oviduct.

As used herein, “prostaglandin antagonist” includes chemical compounds that interfere with the action of prostaglandin, such as aspirin and flunixin meglumine, and chemical compounds that are prostaglandin receptor antagonists which interact with a prostaglandin receptor, such as AL-8810 (Cayman Chemical Co., Ann Arbor Mich.), an 11β-fluoro analog of PGF_(2α), described in Griffen, B. W., Klimko, P., Crider, J. Y., et al., J Pharmacol Exp Ther, 290:1278-1284 (1999). Thus, the term “prostaglandin antagonist” includes both chemical compounds that antagonize the action of prostaglandin itself by any means and those that antagonize the action of prostaglandin by interacting with a prostaglandin receptor. The term “prostaglandin receptor antagonist”, as used herein, refers specifically to a chemical compound that interacts with a prostaglandin receptor. Chemical compounds that interfere solely with the synthesis of prostaglandins, such as by interfering with the action of prostaglandin synthetase, but which do not interfere with the action of prostaglandins are not included within the definition of prostaglandin antagonist as used in this specification.

The invention provides a substantial benefit as the various embodiments of the invention provide an increase in the pregnancy rate following embryo transfer. The invention provides a further benefit as the invention reduces or eliminates the need to treat a recipient female human or animal with a prostaglandin antagonist. Treatment of recipient animals is expensive and labor intensive and the results are subject to individual variation. By providing a method for reducing embryonic death due to exposure to PGF₂, by treating embryos before transfer, the invention provides a substantial savings in cost and labor, as well as better results, that is higher pregnancy rates, than are attainable by treatment of recipient female animals.

The invention may be practiced in any mammalian species in which embryo transfer or in vitro fertilization is feasible. Although the invention is described herein in reference to cattle (Bos species), those skilled in the art will recognize that the invention is applicable to other bovines, such as water buffalo, and other mammals as well. Examples of mammals for which the invention is suitable include humans and other primates such as monkeys and apes, perissodactyla such as horses and rhinoceros, artiodactyla such as pigs, cattle, sheep, goats, camels, llamas, and hippopotamus, carnivora such as dogs, cats, bears, mink, and weasels, pinnipedia such as seals and sea lions, lagomorpha such as rabbits and hares, rodentia such as squirrels, rats, and mice, cetacea such as whales, dolphins, and porpoises, and proboscidea such as elephants.

It has been discovered that PGF_(2α) receptors are present on morula-stage embryos. Although wishing not to be bound by theory, it is conceived that PGF_(2α), acting through such PGF_(2α) receptors, disrupts formation and/or function of junctional complexes between blastomeres, resulting in an interference with continued embryo development. It is further conceived that a prostaglandin antagonist, and preferably a prostaglandin receptor antagonist, when exposed to an embryo in accordance with the invention, inhibits or prevents binding of PGF_(2α) to such receptors, thus preventing or reducing the disruption of the formation and/or function of the junctional complexes and reducing or eliminating this interference with continued embryo development.

The exposure of the embryo to the prostaglandin antagonist may be at any time after collection of an embryo from a donor animal or in vitro fertilization of an oocyte to produce an embryo and before transfer of the embryo to a recipient animal. Thus, the prostaglandin receptor antagonist may be contained in a wash solution to which an embryo is exposed. Preferably, the prostaglandin receptor antagonist is contained in one or more media, such as oocyte maturation media, or collection, culture, or transfer media, in which the embryo is situated between the collection and/or culture and the transfer into the reproductive tract of a recipient animal.

For example, the embryo may be exposed to a prostaglandin antagonist that is contained in one or more of a holding, washing, culture, transfer, manipulation, freezing, or maturation medium. Alternatively, and less preferably, the embryo may be exposed to a prostaglandin antagonist that is contained within a fluid with which the embryo or oocyte is bathed or washed before or after placement of the embryo into a medium or transfer of the embryo into the recipient female.

The concentration of the prostaglandin antagonist to which the embryo or oocyte is exposed and the time during which the embryo or oocyte is exposed to the prostaglandin antagonist may vary depending on several variables, including the nature of the medium or wash fluid in which the prostaglandin receptor antagonist is contained, the particular prostaglandin receptor antagonist to which the embryo is exposed, and whether the embryo or oocyte is immersed in the fluid or medium or alternatively if the medium or fluid flows over the embryo or oocyte.

The prostaglandin antagonist that is useful for the method of the invention is a chemical compound that inhibits the action of a prostaglandin, such as by interfering with the binding of the prostaglandin to a prostaglandin receptor. Thus, the prostaglandin antagonist that is suitable for the invention may be a general prostaglandin antagonist, such as flunixin meglamine, aspirin, or omega-3 fatty acids.

In a preferred embodiment, the prostaglandin antagonist is a chemical compound that selectively inhibits PGF_(2α), and preferably does not substantially interfere with the activity of Prostaglandin E (PGE). PGE is a smooth muscle stimulator which has opposite effects from those of PGF_(2α) on the corpus luteum and embryo. In contrast to PGF_(2α), PGE has antiluteolytic action in that it inhibits the luteolysis that is induced by PGF_(2α).

An example of a selective prostaglandin receptor antagonist that is useful for the invention is AL-8810 (11β-fluoro-15-epi-15-indanyl-tetranor PGF_(2α)) (Cayman Chemical Co., Ann Arbor Mich.), an 11β-fluoro analog of PGF_(2α). Examples of other prostaglandin receptor antagonists include AL-3138 (11-deoxy-16-fluoro PGF_(2α)), THG 113 (see, Peri KG, et al, Semin Perinatol. 26(6):389-397 (2002), and phloretin. Other selective PGF_(2α) antagonists and PGF_(2α) receptor antagonists, known and yet to be discovered, are also suitable for the invention.

In accordance with a preferred embodiment of the method of the invention for protecting an embryo to be transferred to the uterus of a recipient female animal, an embryo that is to be transferred into the uterus of a recipient female animal is exposed to the prostaglandin receptor antagonist at a time that is during and/or after the embryo is collected from a donor animal and before the embryo is transferred into the recipient female. The embryo may be one that is pre-compacted, compacted, or post-compacted such as a blastocyst. Typically, the exposure of the embryo to the prostaglandin antagonist is by holding, washing, culturing, freezing, or transferring the embryo in a culture medium in which is incorporated one or more prostaglandin antagonists. The prostaglandin antagonist is preferably a selective blocker of PGF_(2α). The embryo is exposed to the prostaglandin antagonist for a time and at a concentration that is effective to protect the embryo, completely or partially, from the embryotoxic effects of PGF_(2α).

In accordance with a preferred embodiment of the method of the invention for performing embryo transfer, an embryo to be transferred is exposed to a prostaglandin antagonist at a time between, or during, collection of the embryo from a donor animal or culture of an oocyte in vitro to produce an embryo and transfer of the embryo to a recipient animal, and the embryo is then transferred into the uterus of the recipient animal. Typically, the exposure of the embryo to the prostaglandin receptor antagonist is in vitro by holding, culturing, freezing, or transferring the embryo in a collection or culture medium in which is incorporated one or more prostaglandin antagonists. The prostaglandin antagonist is preferably a selective blocker of PGF_(2α). The embryo is exposed to the prostaglandin antagonist for a time and at a concentration that is effective to protect the embryo, completely or partially, from the embryotoxic effects of PGF_(2α). Any method of collecting an embryo from a donor animal, any method of fertilizing an oocyte to produce an embryo, any method of preparing an embryo for transfer into the uterus of a recipient animal, and any method of transferring an embryo into the uterus of a recipient animal, whether such methods are presently known or are later discovered, are suitable for this method of the invention.

In accordance with the medium of the invention, the medium may be, for example, for maturation of an oocyte that is to be fertilized and transferred into the uterus of a recipient female animal, or for holding, collecting, culturing, freezing, treating, or transferring an embryo that is to be transferred into the uterus of a recipient female animal. The medium of the invention contains components necessary for its utilization as such a medium and, in addition, contains a prostaglandin antagonist at a concentration that is effective to protect an embryo that is situated in the medium from the embryotoxic effect of PGF_(2α) that may be encountered following transfer of the embryo into the uterus of the recipient female.

In accordance with the non-human embryo of the invention, the embryo is a mammalian embryo that is situated inside or outside of a female animal and is exposed, or has been exposed, to a prostaglandin antagonist such that the embryo is protected against embryotoxic effects of PGF_(2α) that may be encountered upon transfer of the embryo into the uterus of a female animal.

The invention is further described by the following non-limiting examples.

EXAMPLE 1

Evaluation of Direct Effects of PGF_(2α) on Embryos

Because studies in the prior art regarding PGF_(2α) and embryonic development were performed in vivo, the possibility exists that the embryonic effects of PGF_(2α) that were reported were due to an indirect effect of PGF_(2α) rather than a direct effect on the embryos. Therefore, studies are performed to determine if direct effects of PGF_(2α) occur on embryonic development during culture of pre-compacted (in vitro-produced) or compacted (in vivo-produced) embryos.

Example 1.a Pre-Compacted Embryos

Embryos are produced by a modified protocol for in vitro production of embryos described by Edwards and Hansen, Biol. Reprod. 55:340-346 (1996). Pre-compacted 16- to 32-cell stage embryos are rapidly washed in KSOM media (Biggers, J. D. 1991. J. Reprod. Fertil. 91:543) supplemented with polyvinyl alcohol (PVA) 3 mg/ml (0.3%). The embryos are evaluated for quality (normal shape, defined blastomeres, extruded blastomeres, cytoplasmic fragmentation, even cytoplasm), are evenly sorted in four groups (formed by embryos of good quality), are transferred to experimental treatments in a 4-well plate as described below, and are returned to the incubator (5.5% CO₂, 7% O₂, and 87.5% N₂ at 38.5° C.). Embryos remain in each treatment for 4 additional days. Embryo development is assessed using IETS (International Embryo Transfer Society) guidelines for classification of bovine embryos.

Dilutions (i.e., treatments) of PGF_(2α) (Cayman Chemical Co.; Ann Arbor, Mich.) are prepared to obtain 0, 1, 10 and 100 ng/mL. Treatments are placed in each well of a 4-well plate (500 μL/well) and equilibrated in the incubator (5.5% CO₂, 7% O₂, and 87.5% N₂ at 38.5° C.) for at least 5 h prior to embryo placement. For each replicate, two media samples from each treatment are collected to determine concentrations of PGF_(2α) by radioimmunoassay (RIA). The first sample is collected on the day in which treatments begin (approximately day 5 of culture) and the second sample obtained after determination of blastocyst development (day 9 of culture).

A total of 7 replicates are utilized. In each replicate, embryos at 16- to 32-cell stage are placed in KSOM media supplemented with 0.3% PVA and receive one of the following culture treatments: 1) control (n=168); 2) 1 ng/mL PGF_(2α) (n=143); 3) 10 ng/mL PGF_(2α) (n=168); 4) 100 ng/mL PGF_(2α) (n=136), and 5) 5 ng/mL PGE₂ (n=62). Prostaglandin E₂ is thought to be a “beneficial” prostaglandin during embryo development (Biggers et al. Biol. Reprod. 19:519-533. (1978)). Therefore, embryos cultured in media with addition of 5 ng/mL of PGE₂ are considered to be a positive control group (Gurevich et al., Reprod. Fertil. Dev. 5:281-283 (1993)) and to ascertain if any effects are associated simply with prostaglandins, per se.

Data are analyzed to test for blastocyst development and hatching rates using an incomplete block design and a randomized block design, respectively. Analysis of variance is performed using mixed models (SAS 8.02, SAS Institute Inc., Cary, N.C.) and contrasts are tested to identify differences across levels of PGF_(2α) on embryonic development. Analyses are then validated with Chi-square analysis (SAS 8.02, SAS Institute Inc., Cary, N.C.).

Results indicate that culture of 16- to 32-cell pre-compacted (in vitro-produced) embryos with 1, 10 or 100 ng/mL of PGF_(2α) in the medium reduced blastocyst development when compared to control (P=0.002). Furthermore, blastocyst development does not differ between control and PGE₂ treatments (P>0.10). Thus, addition of PGF_(2α) to culture medium has a direct negative effect on development of 16- to 32-cell in vitro-produced embryos to blastocyst.

Example 1.b Compacted Embryos

In vivo-derived glycerol-frozen morula-stage bovine embryos are thawed utilizing a three-step glycerol removal procedure. After washing, embryos are allowed to regain normal morphology for 30 min in Vigro holding medium and are sorted by stage of development and quality according with the IETS guidelines for classification of bovine embryos. For this study, a total of 4 replicates are used.

Schrick, et al, Biol. Reprod. 49:617-621 (1993) reported 0.64 ng/mL of PGF_(2α) in flush media from short cycle cows and a negative association of PGF_(2α) concentration with embryo quality. Based on these findings, concentrations of 0 (control, KSOM-PVA), 0.1, 1, and 10 ng/mL of PGF_(2α) in culture medium are selected as treatments. Each treatment is placed in a different well of a 4-well plate (500 μL/well) and then maintained in the incubator (5.5% CO₂, 7% O₂, and 87.5% N₂ at 38.5° C.) for at least 5 h before placement of embryos to allow equilibration of medium. At the same time, media samples from each treatment are collected and stored at −20 C° for determination of PGF_(2α) concentrations by radioimmunoassay (RIA).

Morula embryos (Stage 4) of quality grade 1, 2 or 3 are rapidly washed four times in KSOM-PVA and randomly assigned to one of four treatments: 1) control (n=110); 2) 0.1 ng/mL PGF_(2α) (n=108); 3) 1 ng/mL PGF_(2α) (n=109), 4) 10 ng/mL PGF_(2α) (n=109) and are placed in the incubator (5.5% CO₂, 7% O₂, and 87.5% N₂ at 38.5° C.). After culturing embryos for 24 h in their respective treatment, embryos are washed and placed in KSOM-BSA without PGF_(2α) for an additional 48 h. Evaluation of embryo development using IETS guidelines for classification of bovine embryos is performed by experienced technicians uninformed of treatments. Data are analyzed as in Example 1.a.

Results of this study show that development of compacted (in vivo-derived) morula stage embryos, at least two stages beyond morula utilizing IETS guidelines for development, does not differ between treatments (P>0.10). However, culture of embryos in 0.1, 1, or 10 ng/mL of PGF_(2α) for 24 h shows decreased hatching rates when compared to control (P=0.05).

Example 2

Presence of PGF_(2α) Receptor Transcripts in Morula-Stage Embryos

Embryos are produced in vitro as described above. On day 6 of embryonic development, morula stage embryos are transferred to an “X” plate containing pre-warmed PBS supplemented with 0.1% PVA (polyvinyl alcohol, Sigma; St. Louis, Mo.). Embryos are washed twice in the same solution and then placed in a 1.5 mL RNAse-free eppendorf tube containing 50 μL of RNA later solution (Ambion Inc., Austin, Tex.). Pools of approximately 20 embryos in RNA later are kept at 4° C. overnight and stored at −80° C. until RNA isolation and further processing.

The Absolutely RNA Nanoprep Kit (Stratagene, La Jolla, Calif.) is used to isolate highly pure total RNA from bovine embryos as described by the manufacturer's instructions. In order to decrease the viscosity of RNA later, 70 μl of nuclease free water are added to each sample. Samples are spun at 7,000 g for 5 min and the supernatant removed. Embryos are then lysed by addition of a combination of β-mercaptoethanol and lysis buffer. Following cell lysis, the sample is transferred to a nano-spin cup where the RNA binds to a silica-based fiber matrix. Contaminant DNA is removed by a Dnase digestion step using Dnase I enzyme. Then, a series of high and low salt buffer washes removes Dnase I enzyme and other proteins. Lastly, highly pure RNA is eluted from the fiber matrix with 10 μL of a low-ionic-strength buffer. Elution samples are kept at −80° C. until use.

As a positive control, total RNA from bovine tongue epithelium is isolated using Trizol Reagent (Invitrogen, Carlsbad, Calif.). Epithelial cells are obtained from a fresh tongue by slicing off the epithelium in sections less than 0.5 cm thick and placing them into RNA later solution. Tongue samples are then placed at 4° C. overnight and kept at −80° C. until use. To isolate RNA, 100 mg of tongue epithelium are placed in a 17×100 mm polypropylene tube containing 1 mL of Trizol and tissue samples are homogenized using a power homogenizer (Tekmar's Tissumizer, Tekmar Co., Cincinnati, Ohio). Homogenized samples are incubated for 5 min at room temperature followed by the addition of 0.2 mL of chloroform. Tubes are vigorously shaken by hand for 15 sec and incubated at room temperature for 15 min. Samples are then centrifuged at 12,000 g for 10 min at 4° C. After centrifugation, the aqueous phase is transferred to a fresh tube, where RNA is precipitated by the addition of 0.5 mL isopropyl alcohol and incubation of the samples at room temperature for 15 min. Samples are centrifuged at 12,000 g for 10 min at 4° C., the supernatant is removed and the resulting RNA pellet is washed once using 75% ethanol. Finally, the RNA pellet is air-dried for 5 min, dissolved in 50 μl of nuclease free water and stored at −80° C. until use.

In each of 4 replicates, isolated RNA from 20 compacted morula embryos and 180 ng total RNA from bovine tongue epithelium are reverse transcribed into cDNA in a total volume of 25 ill. The reaction mixture consists of 1× RT buffer, 5 mM MgCl₂, 1 mM of each dNTP, 0.25 nM random hexamers, 20 iu RNase inhibitor, and 100 iu murine leukemia virus reverse transcriptase (MMLV-RT). All reagents used for the RT reaction are purchased from Promega (Madison, Wis.). The RT reaction is carried out at 25° C. for 10 min, and then at 42° C. for 1 h followed by a denaturation step at 99° C. for 5 min and flash cooling to 4° C. As negative controls, tubes are always prepared in which reverse transcriptase is omitted during the RT reaction.

Presence of PGF_(2α) receptor is analyzed by Real Time PCR. Using isolated RNA from in vitro-derived morula-stage embryos, three Real Time PCR replicates are conducted to determine PGF_(2α) receptor transcripts. In each replicate, 10 equivalent embryo (1 equivalent embryo=percentage of the volume from the RT reaction employing one embryo in a defined volume) per tube are utilized to determine the expression of each transcript. Polymerase chain reaction is performed using the iCycler iQ™ Real-Time PCR detection system (Bio-Rad, Hercules, Calif.) and the iQT™ SYBR Green Supermix (Bio-Rad, Hercules, Calif.). The PCR reaction mixture contains of 25 μl 1× iQ Supermix (100 mM KCl, 40 mM Tris-HCl, pH 8.4, 0.4 mM of each dNTP, iTaq DNA Polymerase 50 units/ml, 6 mM MgCl₂, SYBR Green I, 20 nM fluorescein, and stabilizers), 1 μM concentration of forward primer, 1 μM concentration of reverse primer, 4.5 nuclease free water, 10 μl of template from RT reaction, and 0.5 μl of fluorescein. Negative control for each primer set consists of PCR reaction mixture without the inclusion of cDNA.

Histone A₂ amplification is used as a standard control of the Real Time PCR. The Real Time PCR protocol includes an initial step of 95° C. for 15 min followed by 40 cycles of 95° C. for 15 sec, 55° C. for 30 sec, and 72° C. for 30 sec. Fluorescence data are acquired during the elongation step. The melting temperatures of PGF_(2α) receptor and histone A₂ genes are 84° C. and 90° C., respectively. Therefore, melting curve analysis shows a sharp peak at the expected Tm of the various products. The melting protocol is performed by holding temperature at 45° C. for 60 sec and then heating from 45 to 94° C., holding at each temperature for 5 sec while monitoring fluorescence. Product identity is confirmed by ethidium-bromide-stained 2% agarose gel electrophoresis in 1× TBE buffer (90 mM Tris, 90 mM borate, 2 mM EDTA, pH 8.3; FIGS. 1 and 2). In addition, amplicon identity of PGF_(2α) receptor is confirmed by DNA sequencing of Real Time PCR fragments.

The RT-RT-PCR analysis demonstrates that PGF_(2α) transcripts are present in embryos during early development. Positive control PGF_(2α) transcripts from bovine tongue epithelium are readily apparent on ethidium-bromide-stained agarose gel and from in vitro produced bovine embryos.

Example 3

Effect of a PGF_(2α) Receptor Antagonist on In Vitro Development of Embryos

Pre-compacted 16- to 32-cell stage bovine embryos (day 4 post fertilization) are washed in KSOM-PVA and divided into four groups, each of which is cultured for 48 hours in KSOM-PVA containing one of the following: (1) 1000 nM AL-8810, n=95 (AL-8810 group); (2) 1 ng/ml PGF, n=91 (PGF group); (3) 1000 nM AL-8810+1 ng/ml PGF, n=90 (AL-8810+PGF group); or (4) KSOM-PVA without AL-8810 or PGF, n=84 (Control group).

Following the 48 hour culture, embryos from each group are placed in HEPES-TALP and embryonic development is assessed by a technician who is uninformed of the treatments of the embryos in each group. Embryos from each treatment group are washed in KSOM-PVA and transferred to a 4-well plate with KSOM-PVA for further culture until day 8 post fertilization, when embryonic development is again assessed.

Data indicates that addition of PGF on days 4 to 6 decreases the percentage of embryos reaching blastocyst stage on day 8. However, addition of AL-8810 to the culture medium decreases the negative effects of PGF on embryonic development and restores embryonic development to values similar to those of the Control group.

Example 4

Dose Response Study

Pre-compacted 16- to 32-cell stage bovine embryos (day 4 post fertilization) are washed in HEPES-TALP and divided into four groups, each of which is transferred to treatments in a 4-well plate containing 500 ul of KSOM-PVA (0.3%) and returned to the incubator for 96 hours. Incubation conditions are 5.5% CO₂, 7% O₂, and 87.5% N₂ at 38.5° C. The four groups are as follows: (1) KSOM-PVA+AL-8810 at 1000 nM, n=93 (High AL-8810 group); (2) KSOM-PVA+AL-8810 at 500 nM, n=95 (Medium AL-8810 group); (3) KSOM-PVA+AL-8810 at 250 nM, n=93 (Low AL-8810 group); and (4) KSOM-PVA with an equivalent volume of DMSO (dimethylsulfoxide) as used for the first three groups, n=95 (Control group). Following the 96 hour incubation, embryos from each group are placed in HEPES-TALP and embryonic development is assessed by a technician who is uninformed of the treatments of the embryos in each group.

Data indicates that addition of three different concentrations of the prostaglandin inhibitor AL-8810 to culture medium on days 5 through 8 after fertilization does not decrease or increase early embryonic development of pre-compacted embryos when compared to a control group. When only the High AL-8810 and the Control group are analyzed, there is a significant difference in these two groups (60.3%+/−3.9% (High AL-8810 group) vs. 49.9+/−3.9% (Control group); p<0.05).

Example 5

Pre-Treatment of Embryos Before Transfer

Approximately 100 embryo recoveries are performed on day 7 after estrus in beef and dairy cows (lactating and dry). Cows are superovulated (Folltropin) and embryos recovered, evaluated, and frozen (1.5 M Ethylene Glycol; EG) as previously reported (Schrick et al., Biol. Reprod. 49:617-621 (1993)). Half of the embryo recoveries occur utilizing 1 L of each of the following alternative media preparations: 1) Embryo recovery (flush) media (CON, n=50 recoveries; Dulbecco's PBS+1% FCS; GibcoBRL, Cat.# 21300-025; Grand Island, N.Y.) or 2) Embryo recovery (flush) media+AL-8810 (TRT, n=50 recoveries; 430 nM of AL-8810).

Following filtering, embryo dishes are searched, embryos removed (placed in Vigro), and evaluated for quality and development (IETS guidelines). One half of recovered embryos of acceptable development and quality (1-3; IETS) from each flush are frozen individually for direct transfer using 1.5 M EG supplemented with 1) Vigro (F/T Control, n=250 embryos) or 2) Vigro+AL-8810 (F/T Treated, n=250 embryos). Embryos are placed in their respective F/T media treatment for a period of less than 5-10 min following evaluation and before placement in the freezing unit (BioCool controlled rate freezer; FTS Systems, Inc.; Warren, Mich.). Following placement into labeled (Embryo ID) 0.25 mL straws, embryos are frozen (seeding −6° C.; freezing rate:−0.5° C./min) to −32° C., and plunged into a liquid nitrogen storage tank. Embryos remain in the tank for no less than two weeks before transfer to acceptable recipient animals.

Over a two year period, recipient animals (dairy and beef cows and heifers; n=500) have estrus synchronized utilizing GnRH/CIDR/Estrumate protocol consisting of administration of 100 ug GnRH (Cysterolin; Merial) and CIDR (intravaginal progesterone releasing device; Pfizer) insertion on day 0, CIDR removal and injection of 2 mL Estrumate (Schering-Plough Animal Health) on day 7, and estrous detection (twice daily) from days 8 through 12. Seven days after detection of a synchronized estrus, animals are placed in cattle handling facility, blood collected via tail vein for progesterone concentrations (P4 conc. determined as described by Seals et al., 1998), corpus luteum (CL) palpated for acceptability and location, and the embryo placed (embryo transfer, ET) in the upper one half of the uterine horn ipsilateral to the CL (Schrick et al., 1993). Embryos used for ET are thawed (10 sec air thaw; 30 sec in 25° C. water bath), straw labeling (embryo ID) information recorded, and recipient ID collected.

Embryos recovered from beef cattle donors are placed in beef recipients (Angus) and embryos from dairy cattle donors are placed only in dairy recipients (Holstein). On days 21-28, recipients are scanned using transrectal ultrasonography for determination of pregnancy. All animals are palpated rectally 90-150 days after transfer for final pregnancy call. At calving, calves are evaluated for health and gross abnormalities, weighed, identification tag inserted, and sex recorded.

The results of this study establish that the addition of a PGF_(2α) antagonist to media in which an embryo resides, such as the embryo recovery and/or freezing/transfer (F/T) media, increases pregnancy rates of embryos placed in acceptable recipients. No abnormalities are observed in the calves resulting from the pregnancies.

Further modifications, uses, and applications of the invention described herein will be apparent to those skilled in the art. It is intended that such modifications be encompassed in the claims that follow. 

1. A method for protecting a mammalian embryo that is to be transferred into the reproductive tract of a recipient female animal comprising exposing the embryo to a chemical compound that is a prostaglandin antagonist in an amount and for a time sufficient to protect the embryo from the embryotoxic effects of prostaglandin F_(2α).
 2. The method of claim 1 wherein the embryo is exposed to the prostaglandin antagonist during the time the embryo is in a medium in which is incorporated the prostaglandin antagonist.
 3. The method of claim 1 wherein the embryo is a bovine embryo.
 4. The method of claim 1 wherein the embryo is selected from the group consisting of a pre-compacted embryo, a compacted embryo, and a post-compacted embryo.
 5. The method of claim 1 wherein the embryo is a blastocyst.
 6. The method of claim 1 wherein the prostaglandin antagonist is a selective antagonist of prostaglandin F_(2α).
 7. The method of claim 1 wherein the prostaglandin antagonist is a prostaglandin receptor antagonist.
 8. A method for performing embryo transfer comprising obtaining an embryo to be transferred into the uterus of a recipient female animal, exposing the embryo to a prostaglandin antagonist in an amount and for a time sufficient to protect the embryo from the embryotoxic effects of prostaglandin F_(2α), and then transferring the embryo into the uterus of the recipient female animal.
 9. The method of claim 8 wherein the embryo is exposed to the prostaglandin antagonist during the time the embryo is in a medium in which is incorporated the prostaglandin antagonist.
 10. The method of claim 8 wherein the embryo is a bovine embryo.
 11. The method of claim 8 wherein the embryo is selected from the group consisting of a pre-compacted embryo, a compacted embryo, and a post-compacted embryo.
 12. The method of claim 8 wherein the embryo is a blastocyst.
 13. The method of claim 8 wherein the prostaglandin antagonist is a selective antagonist of prostaglandin F_(2α).
 14. The method of claim 8 wherein the prostaglandin antagonist is a prostaglandin receptor antagonist.
 15. A medium for use in embryo transfer or oocyte maturation which medium comprises a prostaglandin antagonist at a concentration that is effective to protect an embryo that is situated in the medium or an embryo that results from fertilization of an oocyte that is situated in the medium from embryotoxic effects of prostaglandin F_(2α).
 16. The medium of claim 15 which is selected from the group consisting of media for holding, collecting, culturing, freezing, treating, and transferring an embryo that is to be transferred into a recipient female animal.
 17. The medium of claim 15 wherein the prostaglandin antagonist is a selective antagonist of prostaglandin F_(2α).
 18. The medium of claim 15 wherein the prostaglandin antagonist is a prostaglandin receptor antagonist.
 19. A non-human mammalian embryo that has been exposed to a prostaglandin antagonist in an amount and for a time effective to protect the embryo against embryotoxic effects of prostaglandin F_(2α).
 20. The embryo of claim 19 wherein the embryo is a bovine embryo.
 21. The embryo of claim 19 wherein the embryo is selected from the group consisting of a pre-compacted embryo, a compacted embryo, and a post-compacted embryo.
 22. The embryo of claim 19 wherein the embryo is a blastocyst.
 23. The embryo of claim 19 wherein the prostaglandin antagonist is a selective antagonist of prostaglandin F_(2α).
 24. The embryo of claim 19 wherein the prostaglandin antagonist is a prostaglandin receptor antagonist. 